(a) Field of the Invention
The present invention relates to a process and an apparatus for the production of synthetic polymers which contain additives.
Said polymers generally are high molecular weight linear polymers which are thermoplastic and are adapted in particular for the production of filaments and fibres by melt spinning. The class of such polymers to which the invention applies more particularly but not exclusively, is that of the polyamides.
(b) Description of Prior Art
It is well known to add to the polymers and in particular to the polyamides, additives having various purposes, in a phase in which the polymer has already been formed and is in the molten state and before shaping operations such as in particular spinning. Said additives may have various functions. One class thereof is the class of the antistatics, which may be constituted particularly by polyolefine, such as polyethylene or polypropylene or mixtures thereof, having a suitable molecular weight. Other classes are constituted by non-fusible materials in the form of solid particles, such as e.g. carbon black, matting agents and pigments.
The addition of additives of the aforesaid or any other types to synthetic linear polymers, in particular polyamides--to which particular reference will be made hereinafter without thereby implying a limitation of the invention--presents some difficulties owing to the high viscosity of the polyamides and the need of obtaining perfectly uniform materials after the mixing. In particular when melt spinning is carried out and the molten polymer is fed from a single source to a plurality of spinning heads or groups of spinning heads, it invariably occurs--when operating according to the known state of the art--that the percentages of additive are not exactly the same in the filaments which issue from the several heads or groups of heads. This causes differences in the properties of the final products, which are extremely undesirable and harmful.